In all mammalian species, gonadotropin-releasing hormone (GnRH) is the first hormone in a complex reproductive cascade. GnRH is released by the hypothalamus and stimulates the secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the pituitary;these gonadotropins then stimulate the gonads to produce sex steroids and follicles/sperm. The actions of GnRH are complex--it is secreted in a pulsatile, as opposed to constitutive, fashion, and at variable frequencies throughout the reproductive cycle. Understanding what signals modulate the developmental fate and secretory actions of GnRH neurons remains a major question for reproductive biologists. This grant proposal will address this issue using a human disease model in which GnRH secretion is defective or absent. Patients with this condition, idiopathic hypogonadotropic hypogonadism (IHH), fail to undergo puberty and are infertile if untreated. Although congenital IHH is a rare disease and family sizes are typically small, a large inbred family of French Canadian descent has been identified with IHH and anosmia. A genome wide scan has been performed and a chromosomal locus for the genetic defect has been identified. In this proposal, the candidate region will be further refined, a complete transcript map for the region will be developed, and RT-PCR will be used to screen the candidate gene for the precise genetic mutation. The mutation spectrum will then be juxtaposed against the baseline clinical/biochemical features of the patients, their neuroendocrine phenotypes, as well as their responses to physiologic replacement with exogenous pulsatile GnRH to develop robust genotype/phenotype correlations. The spatiotemporal pattern of expression of the gene will be studied and in vitro model systems developed to study the physiology of the newly-identified gene. It is hoped that this information will ultimately be used to understand numerous human diseases defined by abnormalities in GnRH secretion, including constitutional delay of puberty, hypothalamic amenorrhea, and central precocious puberty.